Clik here to view.
What’s that magic computation in stb__RefineBlock?
Back in 2007 I wrote my DXT1/5 (aka BC1/3) encoder rygdxt, originally for “fr-041: debris” (so it was size-constrained). A bit later I put up the source and Sean Barrett adapted it into “stb_dxt”,...
View ArticleNotes on FFTs: for users
I was just looking over SIMD FFT code I wrote in 2015 for Bink Audio and Miles Sound System to replace the old, all-scalar implementation we had been using since (presumably) the late 90s. That in turn...
View ArticleNotes on FFTs: for implementers
In the previous post I’ve talked about things you might want to know as someone who uses FFTs, this part covers all kinds of FFT implementation details, including the underlying reasons for a lot of...
View ArticleA very brief BitKnit retrospective
UPDATE May 7, 2023: I wrote this post yesterday somewhat in a huff (for reasons not worth going into) and the original post contained several inaccuracies. These have been corrected in this version and...
View ArticleEntropy decoding in Oodle Data: x86-64 6-stream Huffman decoders
It’s been a while! Last time, I went over how the 3-stream Huffman decoders in Oodle Data work. The 3-stream layout is what we originally went with. It gives near-ideal performance on the last game...
View ArticleClik here to view.
When is a BCn/ASTC endpoints-from-indices solve singular?
This is a result I must have re-derived at least 4 times by now in various ways, but this time I’m writing it down so I just have a link next time. All right. If you’re encoding a BCn or ASTC block...
View ArticleZero or sign extend
A while back I had to deal with a bit-packed format that contained a list of integer values encoded in one of a pre-defined sets of bit widths, where both the allowed bit widths and the signed-ness...
View ArticleInserting a 0 bit in the middle of a value
This one originally came up for me in Oodle Texture’s BC7 decoder. In the BC7 format, each pixel within a 4×4 block can choose from a limited set of between 4 to 16 colors (ignoring some caveats like...
View ArticleBC7 optimal solid-color blocks
That’s right, it’s another texture compression blog post! I’ll keep it short. By “solid-color block”, I mean a 4×4 block of pixels that all have the same color. ASTC has a dedicated encoding for these...
View ArticleClik here to view.
Exact UNORM8 to float
GPUs support UNORM formats that represent a number inside [0,1] as an 8-bit unsigned integer. In exact arithmetic, the conversion to a floating-point number is straightforward: take the integer and...
View Article